Reinforcing fibers such as a glass fiber have been conventionally widely used as a reinforcing material for rubber articles such as a rubber belt, a tire and the like.
The rubber articles such as the rubber belt may be repeatedly subjected to a flexing stress to cause a flex fatigue, resulting in a reduced performance, a peel-off between the reinforcing material and a rubber matrix and a wearing of the reinforcing fiber. Further, the strength is liable to be reduced. Such phenomena tend to be particularly accelerated by a heat and water. In order to prevent a peel-off due to such a flex fatigue and to provide a sufficient reinforcing effect, it is necessary to increase the conformity and adhesion between the reinforcing fiber and the rubber and to provide the rubber article with heat and water resistances. For this purpose, various treating agents may be applied onto the surface of the reinforcing fiber.
For example, in Japanese Patent Application Laid-open No. 221433/89, a treating agent has been proposed which employs, in combination, a water-soluble resorcinol-formaldehyde condensate, a vinylpyridine/butadiene/styrene terpolymer latex, a dicarboxylated butadiene/styrene copolymer latex and a chlorosulfonated polyethylene latex.
The use of such a treating agent makes it possible to satisfy the adhesion between the reinforcing fiber and the rubber matrix and the heat and flex resistances of the treating agent itself to a certain extent, but is accompanied by a disadvantage that when a reinforcing fiber coated with such treating agent is used, sufficiently satisfactory heat, water and flex resistances cannot be obtained because of a insufficient water resistance of the treating agent itself and hence, it is difficult to provide an excellent rubber article.
The present inventors have previously invented and proposed a rubber-reinforcing glass fiber cord coated with a composition consisting essentially of a water-soluble resorcinol/formaldehyde condensate having an improved adhesive strength to a heat-resistant rubber, and a nitrile group-containing highly saturated polymer rubber having an iodine value of 120 or less (see Japanese Patent Application Laid-open No. 270877/88). This invention and proposal have been accomplished by finding that the strength of a rubber film and the adhesive strength to the matrix rubber are enhanced by using a nitrile group-containing highly saturated polymer rubber having an iodine value of 120 or less, preferably 0 to 100.
Even in the above-described invention by the present inventors, a scope for improvement for water and flex resistances has been left.
It is an object of the present invention to provide a reinforcing fiber product in which the disadvantages associated with the prior art are overcome, and which exhibits a large bonding force between a reinforcing fiber and a rubber matrix, and which cannot be reduced in strength, even if it is repeatedly subjected to a flexing stress, and which cannot produce a peel-off between the reinforcing fiber product and the rubber matrix and moreover, has sufficient heat and water resistances.